Production of cyclic imides suitable for oxidation catalysis

ABSTRACT

Disclosed are novel processes for the production of cyclic imide compounds such as N-hydroxyphthalimide (NHPI). The processes may be particularly well-suited for commercial-scale production of cyclic imides such as NHPI. Such cyclic imide compounds are suitable for use as oxidation catalysts, and specifically may be used to oxidize cyclohexylbenzene to cyclohexyl-1-phenyl-1-hydroperoxide. Such an oxidation may be particularly useful in a process for the production of phenol and/or cyclohexanone from benzene via a process comprising hydroalkylation of benzene to cyclohexylbenzene, oxidation of the cyclohexylbenzene to cyclohexyl-1-phenyl-1-hydroperoxide, and cleavage of the cyclohexyl-1-phenyl-1-hydroperoxide to phenol and cyclohexanone. The cyclic imide production process may advantageously include water washing and reactant recovery steps to maximize purity and yield.

PRIORITY CLAIM

This application is a National Phase Application claiming priority toPCT Application Serial No. PCT/US2017/028027 filed Apr. 18, 2017, whichclaims priority from U.S. Provisional Application No. 62/341,971, filedMay 26, 2016. The disclosure of 62/341,971 is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to processes, systems, and apparatus formaking cyclic imide oxidation catalyst, and in particular,N-hydroxyphthalimide (NHPI). The catalyst finds use in many oxidationprocesses. Of particular interest is the oxidation of cyclohexylbenzeneto form cyclohexylbenzene hydroperoxide. Such an oxidation reaction maybe employed as part of a process for making cyclohexanone and/or phenolfrom benzene via hydroalkylation to cyclohexylbenzene.

BACKGROUND OF THE INVENTION

Cyclic imide compounds, and in particular N-Hydroxyphthalimide (NHPI)have many potential uses. In particular, they have shown promise asradical mediators in a number of radical based oxidation reactions, suchthat these compounds can be used to catalyze oxidation reactions, and inparticular to catalyze the oxidation of cyclohexylbenzene tocyclohexyl-1-phenyl-1-hydroperoxide (referred to herein ascyclohexylbenzene-hydroperoxide). As described previously (e.g., in US2014/0148569, US 2013/0211036, and US 2013/0203984), NHPI-catalyzedoxidation of cyclohexylbenzene is particularly advantaged in a processfor making cyclohexanone from benzene via: (i) hydroalkylation of thebenzene to cyclohexylbenzene; (ii) oxidation of the cyclohexylbenzene tocyclohexylbenzene-hydroperoxide; and (iii) cleavage of thecyclohexylbenzene-hydroperoxide to phenol and cyclohexanone.

However, although some basic laboratory-scale chemistry is known for thesynthesis of NHPI, little is known to date about the commercial scaleproduction of NHPI. See, for instance, U.S. Pat. No. 8,658,804, as wellas U.S. Pat. Nos. 4,954,639 and 7,368,615; see also U.S. PatentPublication Nos. 2006/0229196 and 2006/0281629. Thus, it is difficult toobtain quantities of NHPI suitable to catalyze industrial-scaleoxidation reactions, such as the aforementioned oxidation ofcyclohexylbenzene as part of an industrial-scale process for makingcyclohexanone and/or phenol.

There is accordingly a need for processes and systems suitable formaking NHPI (and other cyclic imides suitable as oxidation catalysts) onan industrial scale.

Some further references of potential interest in this regard mayinclude: U.S. Pat. Nos. 4,956,168, 5,472,679, 6,299,734, 6,316,639,7,396,519, and 7,582,774; EP Patent Publication 108294 A, German PatentPublications DE-A-1247282, DE-A-3528463, and DE-A-3601803; JapanesePatent Publications JP 2001-233854, JP 2002-047270, JP 2002-128760, JP2003-081941, and JP 2004-051626; Chinese Patent Publications CN1051170,CN101845012; and WIPO Publication Nos. WO 95/25090, WO 97/22551, WO2014/137623, and WO 2016/053583; and the following publications: (1) L.Bauer and O. Exner, “The Chemistry of Hydroxamic Acids andN-Hydroxyimides,” Angewandte Chemie, International Edition, Vol. 16, No.6, pp. 376-384, 1974; (2) W. R. Roderick and W. G. Brown, “Colorless andYellow Forms of N-Hydroxyphthalimide,” Journal of the Amercian ChemicalSociety, Vol. 79, pp. 5196-5198, 1957; (3) H. Reichelt, C. A. Faunce andH. H. Paradies, “Elusive Forms and Structures of N-Hydroxyphthalimide:The Colorless and Yellow Crystal Forms of N-Hydroxyphthalimide,” J.Phys. Chem. A, Vol. 111, pp. 2587-2601, 2007; (4) M. S. Mannan, “Thermaldecomposition pathways of hydroxylamine: Theoretical Investigation onthe Initial Steps,” J. Phys. Chem. A, Vol. 114, pp. 9262-9269, 2010; (5)Y. Iwata, “Study on decomposition of hydroxylamine/water solution,”Journal of Loss Prevention in Process Industries, Vol. 16, pp. 41-53,2003; (6) Y. Iwata, “Decomposition of hydroxylamine/water solution withadded iron,” Journal of Hazardous Materials, Vol. 104, pp. 39-49, 2003;(7) M. S. Mannan, “Reaction pathways of hydroxylamine decomposition inthe presence of acid/base,” ISBN: 0-8169-0965-2, Paper 538b, presentedNov. 7-12, 2004 at AIChE Annual Meeting in Austin, Tex.; (8) A.Sakakura, R. Yamashita, T. Ohkubo, M. Akakura and K. Ishihara,“Intramolecular Dehydrative Condensation of Dicarboxylic Acids withBronsted Base-Assisted Boronic Acid Catalysts,” Australian Journal ofChemistry, Vol. 64, No. 11, pp. 1458-1465, 2011; (9) Agrawal,“Dissociation Constants of Some Hydroxamic Acids,” Zeitschrift fuerNaturforschung, 1976, Vol. 31B, No. 5, pp. 605-606; (10) Benjamin etal., “The Synthesis of Unsubstituted Cyclic Imides Using HydroylamineUnder Microwave Irradiation,” Molecules, 2008, Vol. 13, pp. 157-169;(11) Edafiogho et al., “Synthesis and Anticonvulsant Activity ofImidooxy Derivatives,” Journal of Med. Chemistry, 1991, Vol. 34, pp.387-392; (12) Einhorn et al., “Mild and Convenient One Pot Synthesis ofN-Hydroxyimides from N-Unsubstituted Imides,” Synthetic Communications,2001, Vol. 31, No. 5, pp. 741-748; (13) Gross et al., “Zur DarstellungVon N-Hydroxyphthalimid Und N-Hydroxysuccinimid,” Journal fur praktischeChemie, 1969, Vol. 311, pp. 692-693; (14) Imai et al., “The Reaction ofN-(Mesyloxy)Phthalimide and N-(Mesyloxy)Succinimide With VariousAmines,” Nippon Kagaku Kaishi, 1975, Vol. 12, pp. 2154-2160; (15)Karakurt et al., “Synthesis of Some 1-(2-Naphthyl)-2-(Imidazole-1-yl)Ethanone Oxime and Oxime Ether Derivatives and Their Anticonvulsant andAntimicrobial Activities,” European Journal of Medical Chemistry, 2001,Vol. 36, pp. 421-433; (16) Khan, “Effect of Hydroxylamine Buffers onApparent Equilibrium Constant for Reversible Conversion ofN-Hydroxyphthalimide to o-(N-Hydroxycarbamoyl)-Benzohydroxamic Acid:Evidence for Occurrence of General Acid-Base Catalysis,” Indian Journalof Chemistry, 1991, Vol. 30A, pp. 777-783; and (17) Sugamoto et al.,“Microwave-Assisted Synthesis of N-Hydroxyphthalimide Derivatives,”Synthetic Communications, 2005, Vol. 35, pp. 67-70.

SUMMARY

In some aspects, the present invention relates to forming solid cyclicimide, for instance N-hydroxyphthalimide (NHPI). Processes according tosome embodiments include contacting hydroxylamine solution with a cycliccarboxylic acid anhydride so as to form a reaction medium having initialtemperature T_(i) of less than 65° C.; raising the reaction mediumtemperature to a transition temperature T_(t) within the range from 65°C. to less than 75° C., thereby forming a first slurry comprising solidintermediate hydroxamic acid within the reaction medium; and furtherheating the reaction medium to a final temperature T_(f) within therange from 75° C. to 200° C., thereby converting at least a portion ofthe solid intermediate hydroxamic acid to solid cyclic imide.

In certain embodiments, the hydroxylamine solution may be obtained bycontacting a hydroxylammonium salt with aqueous base, such as NaOH orNH₃. In further aspects, the cyclic carboxylic acid anhydride comprisesphthalic anhydride, the solid intermediate hydroxamic acid comprisesN-hydroxyphthalamic acid (NHPA), and the cyclic imide comprises NHPI.

Processes in accordance with yet further aspects include a continuousand/or semi-batch reaction. Such reaction may comprise continuouslyfeeding hydroxylamine solution and carboxylic acid anhydride (e.g.,phthalic anhydride) to a continuous flow reactor via one or more feedinlets, so as to establish a reaction medium flowing continuously in adownstream direction within the reactor; at a second location along thereactor that is downstream of the one or more feed inlets, feeding steamor water into the reaction medium; at a third location along the reactorthat is downstream of the second location, feeding additional steam oradditional water into the reaction medium; agitating the reaction mediumwithin the reactor between the second and third locations; andrecovering a reaction product comprising solid cyclic imide (e.g., NHPI)from the reaction medium.

The solid cyclic imide (e.g., NHPI) in processes according to someembodiments is recovered from a reaction product comprising solid cyclicimide in mother liquor. The reaction product may be provided to asolid/liquid separation system so as to obtain the solid cyclic imideand a waste water effluent. The waste water effluent may be furthertreated and/or recycled to the reaction. The solid cyclic imide may beutilized in an oxidation reaction, and in particular embodiments it maybe contacted with cyclohexylbenzene and an oxygen-containing gas so asto obtain cyclohexyl-1-phenyl-1-hydroperoxide.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a process and system for reactinghydroxylamine and cyclic carboxylic acid anhydride in accordance withsome embodiments.

FIG. 2 is a schematic diagram of a process and system for recoveringsolid cyclic imide in accordance with some embodiments.

FIG. 3 is a schematic diagram of a semi-batch reactor system used incarrying out reactions in accordance with the description of theExamples.

DETAILED DESCRIPTION

As used herein, “wt %” means percentage by weight, “vol %” meanspercentage by volume, “mol %” means percentage by mole, “ppm” meansparts per million, and “ppm wt” and “wppm” are used interchangeably tomean parts per million on a weight basis. All “ppm” as used herein areppm by weight unless specified otherwise. All concentrations herein areexpressed on the basis of the total amount of the composition inquestion. Thus, the concentrations of the various components of thefirst mixture are expressed based on the total weight of the firstmixture. All ranges expressed herein should include both end points astwo specific embodiments unless specified or indicated to the contrary.

Nomenclature of elements and groups thereof used herein are pursuant tothe Periodic Table used by the International Union of Pure and AppliedChemistry after 1988. An example of the Periodic Table is shown in theinner page of the front cover of Advanced Inorganic Chemistry, 6^(th)Edition, by F. Albert Cotton et al. (John Wiley & Sons, Inc., 1999).

Various embodiments described herein provide a process for making acyclic imide, such as N-hydroxyphthalimide (NHPI). Taking the example ofNHPI, such processes may include: (1) obtaining reactable hydroxylamine; (2) contacting the reactable hydroxylamine with phthalicanhydride so as to form N-hydroxyphthalamic acid (NHPA); and (3) heatingthe NHPA so as to obtain NHPI. Each of the aforementioned elements ofsuch processes is discussed in further detail below.

Obtaining Reactable Hydroxylamine

“Reactable hydroxylamine” refers to hydroxylamine in suitable form forreaction with phthalic anhydride so as to form NHPA. Hydroxylamine(NH₂OH) is susceptible to being protonated into the correspondinghydroxylammonium ion (NH₃OH⁺), which in turn forms ionic bonds with asalt. However, it is the hydroxylamine itself, not a hydroxylammoniumsalt, that should be reacted with the phthalic anhydride.

In processes according to some embodiments, reactable hydroxylamine maybe obtained in the form of a salt-free water solution, which may also bereferred to as hydroxylamine free base (HAFB), which may be purchased orotherwise acquired (for instance, a 50% HAFB aqueous solution iscommercially available from BASF SE). Such hydroxylamine solution maycomprise (a) 1 wt % to 70 wt % hydroxylamine (such as 5 to 15 wt %, 15to 30 wt %, or 30 to 70 wt %, with ranges from any lower limit to anyupper limit also contemplated), (b) water, and (c) less than 1 wt % ofcompounds other than hydroxylamine and water.

Processes of yet other embodiments include forming an aqueous solutionof hydroxylamine base. For instance, sodium hydroxide (NaOH) and/orother strong bases (e.g., potassium hydroxide (KOH), lithium hydroxide(LiOH), calcium hydroxide (Ca(OH)₂), barium hydroxide Ba(OH)₂, magnesiumhydroxide (Mg(OH)₂), and/or strontium hydroxide (Sr(OH)₂) may be addedto an aqueous solution of hydroxylammonium salt (e.g., aqueoushydroxylammonium sulfate), as shown in the reaction pathway (1) below.It will be appreciated that another hydroxylammonium salt may be usedinstead of, or in addition to, hydroxylammonium sulfate (e.g., thechloride, nitrate, and/or phosphate hydroxylammonium salts, amongothers). Generally, suitable hydroxylammonium salts having meltingpoints (measured at 1 atm pressure) of 100° C. or higher, such that theyare solid at 25° C., 1 atm pressure.

Alternatively, ammonia (NH₃) or another weak base (e.g., methylamine,ethylamine, dimethylamine, diethylamine, methylethylamine (MEA),trimethylamine, triethylamine, sodium acetate, other carboxylic acidsalts, sodium carbonate, sodium bicarbonate, sodium hypochlorite, sodiumphosphate, sodium hydrogen phosphate, and the same salts with potassiuminstead of sodium) may be added to the aqueous hydroxylammonium saltsolution, as shown in the reaction pathway (2) below.

As indicated in each of reaction pathway (1) and (2), both reactionsresult in an aqueous hydroxylamine solution (also comprising anionic-bonded salt).

In yet further embodiments, hydroxylamine solution may be formed bycontacting an aqueous solution comprising hydroxylammonium salt (e.g.,hydroxylammonium sulfate) with a strongly basic ion exchange resin.Examples of suitable strongly basic ion exchange resins are those whichcomprise a hydroxyl group, such that it makes OH⁻ available as a base(similar to the strong base NaOH). More particular examples includestrong base, type 1, anionic resins, for instance macroreticularpolymeric resins. For example, Amberlyst™ A26 resin, available from theDow Chemical Company, is such a resin in which the polymeric resin isbased on crosslinked styrene divinylbenzene copolymer containingpositively charged quaternary ammonium groups. Ionically bonded hydroxylions are part of the resin structure for charge neutrality. In someembodiments, an anionic exchange resin may also have a porous structure,which may be beneficial for use in both aqueous and non-aqueous media.Further, an anionic exchange resin having a macroreticular structure andpore size distribution may impart beneficial resistance to mechanicaland osmotic shock.

In yet other embodiments, the hydroxylamine solution may be formed bycontacting an aqueous solution comprising hydroxylammonium salt with aweakly basic ion exchange resin (e.g., Amberlyst™ A21 resin, availablefrom the Dow Chemical Company, or Lewatit™ MP62WS, available fromLanxess AG). Such resins would function similarly to ammonia solution informing hydroxylamine solution according to some embodiments. The weaklybasic ion exchange resins of some embodiments may more generallycomprise polymeric material comprising one or more neutral ternary aminegroups, such that the amine groups function as weak bases similarly tofree ammonia.

In embodiments in which hydroxylamine solution is formed, thetemperature in solution during formation of the hydroxylamine shouldremain at 40° C. or below, preferably 37° C. or below, more preferably35° C. or below, which is understood to help avoid excessively fastdecay of the hydroxylamine product during reaction. Because the reactionof hydroxylammonium salt and aqueous base is exothermic, someembodiments include processes for managing the temperature of thereaction for forming hydroxylamine solution. For instance, the aqueousbase may be maintained at temperatures of 25° C. or lower, preferably20° C. or lower, more preferably 15° C. or lower prior to contacting thehydroxylammonium salt. Also or instead, a heat exchanger may be used(e.g., around a reaction vessel in which the hydroxylamine solution isformed). However, due to the corrosive nature of the reaction material,it is preferable to control the heat of the aqueous base so as tomaintain reaction temperature within the aforementioned ranges.

Also or instead, in certain embodiments, the pH of the solution duringformation of the hydroxylamine preferably remains within the range from8 to 10; however, lower ranges may be acceptable in some embodiments(e.g., ranging from 3 to 10, such as from 5 to 10). Further, it ispreferred that the hydroxylammonium salt and added base be reacted witheach other in amounts such that the hydroxylamine-equivalent mole ratioof (i) hydroxylammonium salt to (ii) added base (either strong, e.g.,NaOH, or weak, e.g., NH₃) in the solution be within the range from 0.5to 1.5, such as 0.8 to 1.2, for formation of the hydroxylamine. The term“hydroxylamine-equivalent mole ratio” means that the number of moles ofhydroxylammonium salt is multiplied by the number of moles ofhydroxylamine released from the hydroxylammonium salt during reactionwith the added base (e.g., NaOH, NH₃, or other base). Thus, in the caseof hydroxylammonium sulfate, (NH₃OH)₂SO₄, two moles of hydroxylamine arereleased per one mole of hydroxylammonium sulfate. Thus, 1 mole ofhydroxylammonium sulfate equals 2 “hydroxylamine-equivalent” moles forpurposes of computing the hydroxylamine-equivalent mole ratio of thehydroxylammonium sulfate salt to the base.

In some embodiments, use of a weak base, and in particular ammonia, ispreferred in forming the aqueous hydroxylamine solution. For instance,use of ammonia or another weak base may help keep the solution withinpreferred pH ranges during formation of the hydroxylamine, and/ormaintain temperature sufficiently low (e.g., within the preferred rangesnoted above), particularly since ammonia has a smaller exotherm inreacting with hydroxylammonium salts like hydroxylammonium sulfate, ascompared to reaction between NaOH (or another strong base) andhydroxylammonium salts. This means that a weak base can be added to thehydroxylammonium salt solution at a higher rate than a correspondingstrong base (e.g., NaOH), due to the lesser degree of heat generation,while still maintaining temperature adequately low to preventdecomposition of the desired hydroxylamine product.

Reaction of Hydroxylamine and Phthalic Anhydride

As noted, once the hydroxylamine solution (preferably aqueoushydroxylamine solution) is obtained as the reactable hydroxylamine, theprocess of some embodiments further includes contacting thehydroxylamine with phthalic anhydride so as to form a liquid reactionmedium (preferably an aqueous liquid reaction medium). Advantageously,the ensuing reaction steps do not require separation of byproduct saltsfrom the hydroxylamine solution. “Byproduct salts” refer to salts formedduring reaction of hydroxylammonium salt and base, such as a sulfatesalt when hydroxylammonium sulfate is the starting hydroxylammoniumsalt, and more particularly ammonium sulfate when ammonia is the basereacted with hydroxylammonium sulfate to form hydroxylamine That is, theaqueous hydroxylamine solution according to some embodiments comprisesbyproduct salts when it is contacted with phthalic anhydride to form theliquid reaction medium. Preferably, such byproduct salts are as solublein water as possible, which makes for greater ease of eventualseparation of the byproduct salts from solid NHPI product (discussed ingreater detail below). According to yet other embodiments, however, thehydroxylamine solution contains fewer than 1 wt %, preferably 0.5 wt %or less, such as 0.1 wt % or less, of byproduct salts (e.g., as is thecase following separation of the salts; or as is the case whenhydroxylamine free base is obtained for use in the following reactionwith phthalic anhydride).

Preferably, both hydroxylamine solution and phthalic anhydride areprovided to a reaction zone (e.g., in pre-mixed feed or via separatefeed mechanisms) in continuous, batch, or semi-batch fashion. In someembodiments, the hydroxylamine solution and phthalic anhydride areprovided in amounts such that the mole ratio of hydroxylamine tophthalic anhydride is within the range from 0.5 to 2, more preferably0.9 to 1.7, such as 1.1 to 1.5.

However the hydroxylamine is contacted with the phthalic anhydride, thereaction medium is preferably agitated so as to help maximize theconversion of phthalic anhydride. Further, the reaction according tovarious embodiments proceeds in two phases (with agitation continuingduring both phases in some embodiments).

In the first reaction phase according to some embodiments, hydroxylaminesolution and phthalic anhydride are contacted so as to react ascompletely as practicable (e.g., preferably achieving 90 wt %, morepreferably 95 wt %, most preferably 99 wt % or more, such as 100 wt %conversion of phthalic anhydride). The product of this reaction is solidN-hydroxyphthalamic acid (NHPA), which forms a paste-like slurry in theaqueous solution reaction medium. However, phthalic anhydride can alsobe hydrolyzed to phthalic acid during the course of this reaction.Accordingly, two competing temperature preferences are at play duringthis first phase reaction: on the one hand, it is preferred to maintaintemperature of the reaction medium during this first phase reactionbelow 75° C., preferably less than or equal to 70° C., more preferablyless than or equal to 67° C., so as to minimize the conversion ofphthalic anhydride to the undesired byproduct phthalic acid; on theother hand, it is also desirable to gradually raise the temperature ofthe reaction medium to a transition temperature T_(t) within the rangefrom a low of 65° C. to a high of less than 75° C. This is becauseachieving such a transition temperature T_(t) in the reaction mediumallows one to approximate that most of the phthalic anhydride has beenreacted (e.g., it is likely that phthalic anhydride conversion is 90 wt% or more, preferably 95 wt % or more, most preferably 99 wt % or more,such as 100 wt %).

Therefore, the first-phase reaction according to such embodimentscomprises: (a) contacting hydroxylamine solution (preferably aqueoushydroxylamine solution) and phthalic anhydride so as to establish areaction medium (preferably a liquid solution reaction medium) having aninitial temperature T_(i) of less than 65° C., such as within the rangefrom 15° C. to 65° C., preferably from 20° C. to 55° C., more preferablyfrom 25° C. to 40° C. (with ranges from any lower end-point to any upperend-point also contemplated in various embodiments); and (b) raising thereaction medium temperature (preferably while agitating the reactionmedium) to a transition temperature T_(t) within the range from 65° C.to less than 75° C. (i.e., 65° C. <T_(t) <75° C.). In some embodiments,the raising (b) is carried out at a rate within the range from 0.01 to500° C./min, such as 0.1 to 100° C./min Preferably, the heating rate atthis stage is within the range from 0.4° C. to 50° C., such as 0.5° C.to 20° C.; however, heating rates within ranges from any aforementionedlower limit to any upper limit are also contemplated in variousembodiments.

The phthalic anhydride in the contacting (a) is preferably in solidform. According to other embodiments, however, phthalic anhydride ismaintained in its molten state for ease of storage and conveying to thereaction; however, given the high melting point of phthalic anhydride(131° C.), such embodiments preferably also include cooling means—e.g.,use of a heat exchanger and/or addition of cold (10° C. or less) waterto form a slurry of phthalic anhydride. A heat exchanger is preferablegiven the possible reaction of phthalic anhydride to phthalic acid towater.

Because the reaction between phthalic anhydride and hydroxylamine isexothermic, some of the heat needed to raise the reaction mediumtemperature to the transition temperature T_(t) may be provided by thereaction itself; however, in some embodiments, additional heat isprovided to the reaction medium. This additional heat may be provided inany suitable manner. In some embodiments, the heat is provided to thereaction medium during the first phase reaction in the form of heatexchangers (e.g., through use of a heating jacket around a reactor),and/or it may be provided through addition of hot water and/or steam tothe reaction medium. As will be discussed in more detail below, somepreferred embodiments include the use of steam to provide heat to thereaction medium during this first phase.

In various embodiments, the reaction medium at this point is apaste-like first slurry comprising solid NHPA. Preferably, thepaste-like slurry is an aqueous slurry, and in addition to the NHPA andwater, it may also comprise byproduct salts (the presence of which waspreviously noted within the hydroxylamine solution of some embodiments)and byproduct phthalic acid (formed during the reaction of phthalicanhydride).

In the second phase of the reaction according to some embodiments, thefirst slurry comprising the intermediate NHPA is further brought to afinal temperature T_(f) within the range from 75° C. to 150° C.,preferably 80° C. to 120° C., most preferably 85° C. to 95° C. (with anylower limit to any upper limit contemplated in various embodiments).This heating brings about conversion of the NHPA to the desired solidNHPI product. Heating to a T_(f) above 150° C. is also contemplated insome embodiments (e.g., to 200° C. or even up to 300° C.), although itis considered not necessary to achieve the desired conversion of NHPA toNHPI. Further, according to some embodiments, it is preferred that theT_(f) range be below 230° C., preferably below 220° C., to as tomaintain the NHPI product in solid form, given the 233° C. melting pointof NHPI.

As NHPA is converted to NHPI, the first slurry of the reaction mediumtransitions to a second slurry that is more difficult to agitate; thus,some embodiments include the addition of water, steam, or other fluid(inert to the hydroxylamine-phthalic anhydride reaction) to the reactionmedium slurry (such fluid may be added before, during, or after theheating of the second phase, preferably before or during). In somepreferred embodiments, the addition of water and/or steam is used bothto further heat the reaction medium and to render the first and/orsecond slurries more easily agitated. In yet other embodiments, however,water may be added to increase stirability without necessarilyincreasing temperature. In fact, water added to increase stirability mayin some embodiments lead to a reduction of the reaction mediumtemperature (e.g., where added water is of lower temperature than thereaction medium); in such instances, heat is separately provided (e.g.,by heat exchange means such as a heating jacket or the like, as is knownin the art) to then raise the temperature to the desired T_(f).

Accordingly, the process of some embodiments further comprises, afterthe previously-noted (b) raising the reaction medium temperature toT_(t), (c) further heating the reaction medium to the final temperatureT_(f) (according to the above-recited ranges for T_(f)), therebyconverting at least a portion, preferably at least 80 wt %, morepreferably at least 90 wt %, even more preferably at least 95 wt %, ofthe NHPA to NHPI. In certain of these embodiments, the (c) furtherheating comprises adding water and/or steam to the reaction medium. pHis preferably maintained at or above 3.5, such as 4.0 or higher, duringthis heating. Likewise, pH of the second slurry comprising NHPI ispreferably maintained at or above 3.5, such as at 4.0 or higher.

The heating rate may be rapid (e.g., the process may comprise heatingthe reaction medium at a rate within the range of 0.01° C./min to 1000°C./min, preferably 300° C./min to 750° C./min, more preferably 400°C./min to 750° C., with ranges from any lower limit to any upper limitalso contemplated in various embodiments). Further, the reaction mediumaccording to some embodiments may be maintained at a temperature withinany of the foregoing ranges noted as suitable for final temperatureT_(f) for a period of time (e.g., at least 5, preferably at least 12,more preferably at least 15 minutes, or in some embodiments within therange from 0 to 60 min) to ensure maximum conversion of NHPA to NHPI. Insome embodiments, this can be accomplished through lapse of time betweenheating and removal of product (e.g., in a batch reactor) or, in otherembodiments, through controlling flow rate in a continuous flow reactor(e.g., a down-flow reactor) so as to achieve a residence time within oneof the foregoing time ranges in a portion of the continuous reactor inwhich the temperature of the reaction medium is within the foregoingranges for T_(f).

Batch, Semi-Batch, and Continuous Reaction

NHPI-forming reactions in accordance with various embodiments may becarried out in batch, semi-batch, or continuous reaction modes.

For instance, in a batch or semi-batch reaction according to someembodiments, the hydroxylamine solution and phthalic anhydride areprovided to one or more batch reaction zones so as to form a reactionmedium in each reaction zone. Each batch reaction zone may comprise astirred tank reactor or any other suitable reactor device capable ofagitating the reaction medium. Each reactor device may comprise aheating jacket, heating coils, or the like disposed on an outer surfaceof the reactor, and/or a water or steam feed conduit capable ofdelivering water and/or steam to the reaction medium in each batchreactor, so as to enable temperature control of the reaction medium.Alternatively (or in addition), the inlet feed conduit may be providedwith a heat exchanger or the like to control inlet feed temperatures(and thereby help control reaction medium temperature). Each reactionzone temperature is preferably monitored so as to ensure initialtemperature T_(i) of the reaction medium is initially maintained withinthe ranges specified previously. Temperature monitoring may be by anysuitable means in the art (e.g., direct measuring and/or calculationbased on inlet and outlet temperatures, or the like). To the extentdifferent means of monitoring temperature within a liquid reactionmedium may differ in their results, the following means of measuringtemperature in the reaction medium in the batch reactor should governfor purposes of determining temperature in a batch or semi-batchreaction medium according to various embodiments described herein: giventhe continuous agitation of the reaction medium, temperature may bemeasured directly using one or more temperature probes (preferablyTeflon-coated type J or type K thermocouple, with no need for athermowell) inserted anywhere in the reaction medium, so long as eachprobe is inserted into the reaction medium such that it has no physicalcontact with a reactor wall, mixing apparatus, or other component of thereactor (i.e., such that the probe is immersed in, and surrounded by,the reaction medium). Where multiple temperature probes are used todetermine temperature of the batch or semi-batch reaction medium, theaverage (mean) temperature of each probe may be taken as the reactiontemperature.

In yet other embodiments, the reaction may be carried out in semi-batchor continuous mode in a reaction system such as the system 101illustrated in FIG. 1, operation of which will be described inconnection with that figure. Hydroxylamine solution (preferably at 40°C. or less, more preferably 37° C. or less, as described previously) maybe supplied to a down-flow reactor 110 in a continuous or semi-batch(e.g., sporadic and metered) manner via hydroxylamine feed conduit 115.Solid phthalic anhydride can be stored in any suitable storage unit(e.g., silo 105 comprising hopper 106 in a bottom portion thereof),metered from the storage unit 105, and fed to the reactor 110 via feedconveyor 116. Feed conveyor 116 may be any suitable means for conveyingsolid feed to the reactor 110, such as a screw conveyor, drag chain,vibratory conveyor, belt conveyor, bucket conveyor, pneumatic conveyor,or other like conveyor. Preferably, feed conveyor 116 enables continuousflow of solid phthalic anhydride feed to the reactor 110, and itfurthermore prevents passage of liquid from the reactor 110 to thestorage unit 105. Feed conveyor 116 as illustrated in FIG. 1 is ascrew-type conveyor.

Many forms of reactors capable of mixing or otherwise agitating thereactor contents could be used in processes according to variousembodiments. Illustrated in FIG. 1 is a down-flow reactor 110 equippedwith a plurality of rotary mixing blades 112 that are turned by a motor111. The rotary mixing blades 112 are interposed between donut-shapedbaffles 113 extending inward from the reactor wall into the innerreactor space, creating a set-up akin to a disk-and-donut reactor design(in which the disks are replaced by rotary mixing blades 112). Inalternatives according to some embodiments, a disk-and-donut design mayinstead be used (in which disks, stationary or rotating, are employed inplace of the rotary mixing blades 112). Horizontal reactor designs couldalternatively be used, as well. Preferably, the reactor is capable ofpermitting flow of the reactor contents in a downstream direction (e.g.,from phthalic anhydride and hydroxylamine feed inlet(s) to productoutlet 120), while also being capable of agitating the reactor contentsin a direction that is at least partially perpendicular to thedownstream flow of reactor contents (e.g., such that at least someportion of mass transfer as a result of the agitation occurs in adirection that is represented by a vector having an angle between 80°and 100° relative to the downstream direction). As illustrated in FIG.1, the downstream direction in the down-flow reactor 110 is downward(i.e., in the direction of gravity), and the rotary mixing blades 112and baffles 113 provide horizontal/radial agitation of the reactionmedium within the upper portion of the reactor 110. As also illustratedin FIG. 1, the reactor 110 of some embodiments may include a downstreamportion 119 in which the mixing apparatus is not disposed.

As the hydroxylamine solution and phthalic anhydride are fed into thetop of the down-flow reactor 110, the reaction medium in the upperportion of the reactor in some embodiments has initial temperature T_(i)in accordance with the previously-described ranges of T_(i). Thereaction medium according to some embodiments will, at this point in thereactor, comprise liquid solution. The mixing apparatus may or may notbe disposed in this upper portion of the reactor 110; as illustrated inFIG. 1, the mixing apparatus is not disposed in this upper portion ofthe reactor 110. At a point downstream of the feed (hydroxylaminesolution and phthalic anhydride feed) inlet(s) to the reactor 110,heating is provided to the reaction medium within the reactor 110. Inembodiments in accordance with FIG. 1, providing heating to the reactionmedium comprises feeding steam to the reactor 110 (e.g., via first steamconduit 131), although it will be appreciated that hot water (preferablyhaving temperature greater than the initial temperature T_(i) of thereaction medium) may be utilized instead or in addition. Temperature ofsteam provided at this point preferably is within the range from 100° C.to 500° C., such as from 100° C. to 250° C., or 100° C. to 150° C., withranges from any lower limit to any upper limit contemplated in variousembodiments. Temperature of hot water provided at this point preferablyis within the range from about 50° C. to 100° C. As illustrated in FIG.1, mixing of the reaction medium begins at this point in the downstreamflow of the contents within the reactor 110. As the reaction mediumheats and conversion of the phthalic anhydride to NHPA increases, thereaction medium will become a first slurry or paste (e.g., within theportion of the reactor 110 in which the rotary mixing blades 112 aredisposed, i.e., the portion downstream of the inlet of the first steamconduit 131 and upstream of the inlet of the second steam conduit 132).Advantageously, use of steam or water to provide the heat to thereaction medium also serves to make this paste-like reaction medium moreeasily agitated. According to some embodiments, in this portion of thereaction medium flowing through the portion of the reactor 110 in whichthe rotary mixing blades 113 are disposed, temperature of the reactionmedium is increased according to the rates of heating from initialtemperature T_(i) to transition temperature T_(t) previously described.

At a point downstream of the inlet of the first steam conduit 131, asecond steam conduit 132 provides additional steam to the reactionmedium within the reactor 110. The additional steam may have temperatureaccording to any of the ranges previously noted with respect to steamprovided by the first steam conduit 131. Alternatively, hot water may beprovided in this second conduit 132, having temperature within the rangefrom 70° C. to 100° C. In some embodiments, the portion of the reactionmedium to which the additional steam is fed is at a transitiontemperature T_(t) (within any of the above-described ranges of T_(t)).As such, it can be approximated that high conversion of the phthalicanhydride (e.g., at least 90, 95, 99, or 100 wt %) of the phthalicanhydride has been achieved in this portion of the reaction medium.Preferably, the distance between the inlets of the first and secondsteam conduits 131 and 132, respectively, is such that residence time ofthe reactor contents between said first and second steam feeds allowsfor the highest practicable conversion of phthalic anhydride to NHPA,while also permitting sufficiently slow heating to minimize sidereactions of the phthalic anhydride to phthalic acid. The ordinarilyskilled artisan will recognize that various parameters may be adjustedinstead of or in addition to distance between the inlets of steamconduits 131 and 132, e.g., flow rate of reactor contents and flow ratesof the respective steam feeds. In certain embodiments, the distancebetween steam feeds, flow rates, and/or other design factors are suchthat the previously described heating rate of the reaction medium frominitial temperature T_(i) to transition temperature T_(t) is maintainedwithin the portion of the reaction medium flowing from the inlet of thefirst steam conduit 131 to the inlet of the second steam conduit 132,and further such that the reaction medium has reached transitiontemperature T_(t) at the point at which the second steam conduit 132provides the additional steam to the reaction medium. Further, althoughnot illustrated in FIG. 1, in certain embodiments, additional conduitsmay deliver additional steam and/or water feeds to the reaction mediumso as to establish a desired temperature profile within the flowingreaction medium.

The additional steam according to some embodiments heats the reactionmedium to the final temperature T_(f), thereby converting the NHPA inthe reaction medium to NHPI.

The reaction medium then flows downstream through the reactor 110 in adownstream portion 119 in which the flow regime approaches plug flow.Just downstream of the inlet of the final steam conduit 132, convectioncurrents continue to distribute heat through the reaction medium,converting NHPA to NHPI. As this conversion takes place, the reactionmedium transitions from the first paste or slurry to a second paste orslurry comprising NHPI as it flows through the reactor 110. Fartherdownstream within the downstream portion 119, the reaction medium beginsto cool once again; this further cooling may help additional solid NHPIprecipitate out of the second slurry. The second slurry then exits thereactor through outlet 120, preferably via a rotary valve 121 or othermeans suitable for conveying the second slurry or paste in continuousflow through the outlet 120, after which the solid NHPI product isseparated from the mother liquor in the second slurry (described in moredetail below).

Accordingly, processes in accordance with embodiments carried out in thesystem illustrated in FIG. 1 may be summarized more generally ascomprising: (a) feeding hydroxylamine solution and phthalic anhydride toa reactor via one or more feed inlets, so as to establish a reactionmedium flowing in a downstream direction within the reactor; (b) at asecond location along the reactor that is downstream of the one or morefeed inlets, feeding steam into the reaction medium; (c) at a thirdlocation along the reactor that is downstream of the second location,feeding additional steam into the reaction medium; (d) agitating thereaction medium within the reactor between the second and thirdlocations; and thereafter (e) recovering a reaction product comprisingNHPI from the reaction medium. Optionally, the reaction medium can beagitated upstream of the second location and/or downstream of the thirdlocation, as well. In some embodiments, the reaction medium upstream ofthe second location (i.e., upstream of the first feeding point of thesteam) will comprise liquid solution (comprising hydroxylamine andphthalic anhydride); the reaction medium will comprise a slurry or paste(comprising NHPA) in a portion of the reaction medium downstream of thesecond location and upstream of the third location; and the reactionmedium will comprise a second slurry or second paste downstream of thethird location. In certain of these embodiments, the reaction mediumapproaches plug flow in the portion of the reaction medium downstream ofthe third location (i.e., downstream of the second steam feed location).

Controlling the Reaction

It should be noted that processes according to many of theabove-described embodiments are not limited to or even necessarilyassociated with reaction medium temperatures (e.g., the initialtemperature T_(i), transition temperature T_(t), and final temperatureT_(f) described previously). For instance, in the case of semi-batch orcontinuous reactions according to some embodiments, maintaining flow ofthe reaction medium in a downstream direction while feeding steam and/orhot water to the reaction medium at the second and third locationsallows for flexible design of the process conditions (e.g., flow ratewithin the reactor, inlet steam flow rate(s), and/or distance betweenthe second and third locations at which first and second steam feeds,respectively, are provided) so as to achieve adequate heating and mixingof the reaction medium between the two steam feed locations. Suchadequate heating and mixing preferably achieves the goals of (i) highestpracticable conversion of phthalic anhydride to NHPA in the reactionmedium while (ii) minimizing the side reaction of phthalic anhydride tophthalic acid. The ordinarily skilled artisan, equipped with theknowledge provided herein, will readily be able to design reactionmedium flow rate (e.g., residence time), reactor agitation, distancebetween steam feeds, and steam flow rates so as to ensure maximumconversion of phthalic anhydride to NHPA while minimizing phthalic acidformation upstream of the second steam feed point (i.e., the thirdlocation in the above summary of processes according to someembodiments). For instance, a target heating rate may be set (e.g.,within the target heating rates according to some embodiments describedpreviously with reference to the heating from initial temperature T_(i)to transition temperature T_(t)), and one or more of first steam feedflow rate, reaction medium flow rate, and reaction agitation, may bedesigned so as to approximate that target heating rate. And, rather thannecessarily requiring attention to reaction medium temperature, theproduct can simply be analyzed to determine if excessive phthalic acidis present (in which case reaction medium flow rate can be slowed,and/or distance between steam feed points increased, and/or agitationmodified to increase mass transfer within the reaction medium betweenthe steam feed points). Or, if unreacted phthalic anhydride remains inthe product, steam flow rate in the first steam feed (i.e., at thesecond location in the above summary) can be increased, and/or reactionmedium flow rate decreased, so as to ensure more complete heating.

Nonetheless, in yet other embodiments, providing heat to the reactionmedium may be associated with reaction medium temperature, and couldeven be controlled in a real-time manner (e.g., usingactuator-controlled valves or like means to decrease or increase feedrates of steam, hydroxylamine solution, and/or phthalic anhydride, basedat least in part upon measured temperature within the reaction medium).For instance, in processes according to such embodiments, a firsttemperature probe may be inserted into the reactor at a location that isboth (i) upstream of the inlet of the first steam conduit 131 and (ii)at a location along the length of the reactor that is within 0.05 Dmeters downstream from the inlet of the hydroxylamine solution feedconduit 115 (where D is the total length of the reactor, e.g., height ofa down-flow reactor or lateral length of a horizontally disposedreactor). The first temperature probe is inserted such that it isimmersed in the flowing reaction medium during normal operation of thereactor 110, and therefore can measure a first temperature of thereaction medium. Preferably, the process in such embodiments iscontrolled such that the first temperature of the reaction medium iswithin one or more of the ranges for initial temperature T_(i), givenpreviously. Likewise, a second probe may be inserted into the reactor110 at a location that is between 0.01 D meters and 0.05 D metersupstream from the inlet of the second steam feed conduit 132, so as tobe immersed in the flowing reaction medium during normal operation ofthe reactor 110, enabling measurement of a second temperature of thereaction medium. Preferably, the process in such embodiments iscontrolled such that the second temperature of the reaction medium iswithin one or more of the ranges for transition temperature T_(t) givenpreviously. Finally, a third probe may be inserted into the reactor 110at a location that is between 0.03 D and 0.08 D meters downstream fromthe inlet of the second steam feed conduit 132, so as to be immersed inthe flowing reaction medium during normal operation of the reactor 110,enabling measurement of a third temperature of the reaction medium.Preferably, the process of such embodiments is controlled such that thethird temperature is within one or more of the ranges for finaltemperature T_(f) given previously. In embodiments in which more thantwo steam inlets are used to create a desired temperature profile withinthe reactor, final temperature T_(f) is instead measured at a point thatis between 0.03 D and 0.08 D meters downstream from the inlet of thefinal steam feed conduit. It should be noted that other means suitablein the art for determining temperature profile within the reactionmedium may instead be employed to determine whether the initial,transition, and final temperatures are reached within the various pointsof the reaction medium; however, to the extent such methods may providesignificantly different results (i.e., differences greater than theordinarily skilled artisan would expect from experimental error), it ispreferred to use the temperature measurement methods described herein.

In yet other embodiments of semi-batch or continuous operation similarto the reactor system 101 illustrated in FIG. 1, instead of (or inaddition to) providing heat through steam and/or water feeds, thereactor 110 could be equipped with a heating jacket, heating coils, orother like heat exchange means capable of providing heat to the reactionmedium. However, heating via steam/water feeds is preferred for at leastthree reasons:

-   -   (1) Due to the corrosive nature of hydroxylamine, the interior        walls of all process pipes and vessels in which hydroxylamine is        or may be present (e.g., reactor 110) must be polymer-lined (for        example, polytetrafluoroethylene (e.g., Teflon coatings),        polyethylene, polypropylene, or the like), and such polymer        lining drastically reduces the efficiency of heat exchange        across such vessel walls;    -   (2) As noted previously, the steam and/or water provide the        extra advantage of rendering the reaction medium within the        reactor 110 more easily agitated as the reactor contents become        more paste-like during the course of the reaction; and    -   (3) It is believed that water and/or steam addition        advantageously helps maintain in solution (i.e., prevents the        precipitation of) any byproduct phthalic acid generated during        the reaction (e.g., through hydrolysis of phthalic anhydride to        phthalic acid), as well as any other salt impurities (such as        sulfate, chloride, or other salts corresponding to the        hydroxylammonium sulfate, hydroxylammonium chloride, or other        hydroxylammonium compound) used in forming the hydroxylamine.

Expanding further on the noted third advantage of water and/or steamaddition according to certain embodiments, hydroxylammonium sulfate andammonia may be preferred reactants for forming the hydroxylamine invarious embodiments, as the corresponding ammonium sulfate saltbyproduct formed from that reaction has advantageously high solubilityin water. Thus, in general, it is preferred that the byproduct of thehydroxylammonium salt and base reaction be as highly soluble in water aspossible, so as to make removal by water washing as efficient aspossible (e.g., such that less water overall is required to remove thesame amount of byproduct). This will help minimize wastewater generatedin washing the solid NHPI product, discussed in greater detail below.

In yet further embodiments, the reaction medium may be monitored fortransition between reaction phases by means other than temperature,product composition analysis, or the like. For instance, viscosity ofthe reaction medium may be monitored to determine the point within acontinuous flow reactor (or the time during operation of a batchreactor) at which the first slurry comprising NHPA intermediate forms;heat can then be provided to form the second slurry comprising NHPI.Optionally, the reaction medium viscosity may be measured to confirmformation of the second slurry following the addition of heat. Otheronline physical measurements may also or instead be carried out (e.g.,density, online particle analyzing, online IR, Raman, particle counters,reflective measurements, online NMR, X-ray, radar, or the like). Suchprocesses may therefore comprise contacting hydroxylamine solution andphthalic anhydride to form a liquid solution reaction medium; allowingthe hydroxylamine and phthalic anhydride to react so as to form a firstslurry comprising NHPA (while maintaining temperature in the liquidsolution and in the first slurry at less than 75° C., preferably 70° C.or less, more preferably 67° C. or less); and heating the first slurryto convert at least a portion (preferably at least 85 wt %, morepreferably at least 90, 95, 99, or even 100 wt %) of the NHPA to NHPI,thereby forming a second slurry comprising the solid NHPI. Heating thefirst slurry may comprise heating to a final temperature T_(f) accordingto any one or more of the previously described ranges for T_(f).

Multiple Reaction Zones

In yet further embodiments, the above-described processes may take placein multiple reaction zones. Advantageously, such reaction zones may besplit according to the stages of the reaction. For instance, some suchembodiments include a first reaction zone capable of receivinghydroxylamine solution and phthalic anhydride feed, and be controlled tohave inlet temperature within any one or more of the ranges for initialtemperature T_(i) previously described. The first reaction zone isfurther controlled so as to maintain temperature below 75° C.,preferably 70° C. or less, or 67° C. or less. The first slurrycomprising NHPA is formed in the first reaction zone, and then conveyedby any suitable means to a second reaction zone. The second reactionzone is operated to heat the first slurry to convert at least a portionof the NHPA (preferably at least 85 wt %, more preferably at least 90,95, 99, or even 100 wt %) to NHPI, thereby forming the second slurry.

Alternatively, in other embodiments, each reaction zone may becontrolled based upon viscosity of the reaction medium, and/orpre-calculated residence times, rather than based upon reaction mediumtemperatures, similar to embodiments described previously.

Recovering Solid NHPI Crystals

The solid crude NHPI crystals resulting from reactions according tovarious of the above-described embodiments may be removed from thesecond slurry by filtration, draining, or the like, and they may furtherbe dried (e.g., oven dried), or processed in any other manner known forthe removal of solid reaction products from a mother liquor.

The removal of crude NHPI crystals from the slurry leaves a firstwastewater effluent, the handling of which is discussed in more detailbelow.

In addition, processes of some embodiments further comprise washing thecrude NHPI crystals with cold water (0° C. to 10° C., such as 2° C. to6° C., preferably 3° C. to 5° C.) to remove various organic andinorganic impurities from the crystals. Such a wash should be sufficientto obtain high purity NHPI crystals, particularly if water and/or steamwere added to the first slurry comprising the NHPA, thereby helping tomaintain various impurities in solution.

Water washing may be particularly advantageous in embodiments whereinthe reactable hydroxylamine was obtained by, e.g., reaction betweenhydroxylammonium salt and base. Such reactions may result in severalimpurities present in the mother liquor (and thus on crude, unwashedNHPI crystal product), including ions (e.g., sodium and/or ammoniumions, or others, depending on the base used in forming reactablehydroxylamine), salts (e.g., sulfate where hydroxylammonium sulfate isthe hydroxylammonium salt), water, phthalic acid, and other organicimpurities. Even in embodiments where salt-free reactible hydroxylaminesolution is used as the starting material, impurities such as phthalicacid and water may exist on the crude NHPI crystals, such that waterwashing in these embodiments may also be useful. However,advantageously, in embodiments in which salt-free aqueous hydroxylaminesolution is contacted with phthalic anhydride, a water wash of theproduced NHPI crystals may be omitted, such that the NHPI crystals arepassed to their further use (e.g., catalyzing an oxidation reaction, asdiscussed below) after separation from the slurry, without additionalwater washing.

In some particularly advantageous embodiments, water washing andseparation of solid NHPI crystals are carried out together. Forinstance, some embodiments include the use of a countercurrent waterwash column to simultaneously wash the crude NHPI crystals and separatethose crystals from the mother liquor. In some such embodiments, secondslurry comprising crude NHPI crystals from processes according tovarious of the previously described embodiments is fed to the top of awash column, while water (preferably with temperature within the rangefrom 0° C. to 30° C., more preferably 0° C. to 10° C.) is flowed upwardthrough the column countercurrent to the downward-flowing slurrycomprising NHPI crystals in mother liquor. The column may includeparallel lamella (e.g., to provide surface area for solids to collect).As the water passes countercurrently to the solids, it removesimpurities such as acids, byproduct salts, and the like. The wet solidsexit the bottom of the vessel. Vacuum pressure may be applied to the wetsolids to assist in further water removal.

In yet other embodiments, water washing and separation of solid NHPIcrystals occurs in a wash and vacuum filtration system 201, such as thatillustrated in FIG. 2. The second slurry comprising crude NHPI crystalsin mother liquor exit the reactor 110 through outlet 120 and arecollected upon a filtration belt 210, which moves in the clockwisedirection in the system 201 depicted in FIG. 2. The filtration belt 210conveys the crude solids over one or more mother liquor vacuum devices212, which aid in removal of the mother liquor from crude solid product.The mother liquor may be collected through the vacuum device(s) 212 aswell. Optionally, and as shown in the system 201, a cold water wash maybe flowed over the crude solid product via wash conduit 220. The waterpreferably has temperature between 0° C. and 30° C., more preferably 0°C. to 10° C., such as 3° C. to 6° C. (which temperature may be obtained,e.g., by passing the water wash through a heat exchanger 221).Advantageously, the water wash may be provided to the crude solids overa mother liquor vacuum device 212, such that the vacuum helps remove thewater and impurities collected in the wash. The wash in turn iscollected through the vacuum device.

The filtration belt 210 may further convey the crude solids to a dryingstage, shown in FIG. 2 as comprising flowing steam and then air over thecrude solids via steam feed 230 and air feed 240 (although any otherinert gas besides air may be used instead, e.g., N₂). Further dryingvacuum devices 231 and 241, respectively, pull the condensing steam andair, respectively, over and out of the crude solid product. As the steamcondenses on the crude solid product, moisture and water-boundimpurities may be drawn out from the crystals to aid in furtherpurification. Flowing air subsequently dries the product and cools itafter contact with the steam. The solid product NHPI crystals may thenbe collected and/or conveyed to storage or to an oxidation reaction(e.g., via screw conveyor 280, or via any other suitable means forconveying solids as discussed previously with respect to conveying solidphthalic anhydride).

Two-phase waste product comprising mother liquor (comprising one or moreof water, byproduct salts, and byproduct phthalic acid from the reactor110), water wash (comprising further impurities washed from the solids,such as additional phthalic acid and/or byproduct salts), condensedsteam, additional moisture, and air (or other inert gas) are collectedin a vacuum conduit 250 in fluid communication with the mother liquorvacuum devices 212 and the drying vacuum devices 231 and 241. A liquidring vacuum pump 251 or other suitable two-phase pumping device in fluidcommunication with the vacuum conduit 250 provides the desired work toexert vacuum pressure on the belt 210 via the vacuum devices 212, 231,and 241. Optionally, the pump 251 may also deliver the two-phase wasteproduct to a separation drum 260 or other suitable vapor-liquidseparation device, so as to vent air or inert gas via vent conduit 261,while recovering liquid waste water (comprising in various embodimentsone or more of byproduct salts, phthalic acid, and water) in wastewaterconduit 265. Optionally, as shown in FIG. 2, a portion of the liquidfrom the wastewater conduit 265 may be split as a recycle stream inrecycle conduit 266 and provided to the reactor 110 at a point justupstream of the outlet 120 (e.g., a distance within the range from 0.001D to 0.05 D upstream of the outlet 120, where D is the height or lengthof the reactor 110). Advantageously, this recycle stream providescooling to the second slurry comprising NHPI, which could aid in furtherprecipitation of NHPI product from the second slurry. To further helpincrease precipitation of solid NHPI product from the second slurry, therecycle stream may be cooled (e.g., by heat exchanger 267).

Waste Water Handling

As noted, solid-liquid separation of the slurry (and, optionally, waterwashing the recovered NHPI solids) produces a wastewater effluent. Thewastewater effluent comprises water, phthalic acid, and possibly alsocomprises byproduct salts (e.g., salts generated during earlierhydroxylammonium salt reaction with base, in embodiments where suchreactions are used to generate the reactable hydroxylamine). In someembodiments, an acid, preferably a strong acid (e.g., sulfuric acid,hydrochloric acid, hydrofluoric acid, etc., preferably sulfuric acid)may be added to the wastewater stream in order to cause precipitation ofsolid phthalic acid from the wastewater solution. This enables phthalicacid recovery by a further solid/liquid separation (e.g., filtration,vacuum filtration, gravity separation, filter press, clarifier, or thelike). The solid phthalic acid may be converted back to phthalicanhydride via dehydration (e.g., using a boronic acid catalyst attemperatures ranging from about 90° C. to 160° C.; or by heating in theabsence of catalyst to 220-270° C.). This additional phthalic anhydridemay be recycled as additional phthalic anhydride feed to be contactedwith the hydroxylamine.

Otherwise, the wastewater may be provided to a water treatment facility,e.g., a biological water treatment facility or the like as would besuitable for removing contaminants (e.g., phthalic acid, byproductsalts) from the water.

Obtained NHPI Crystals

The NHPI crystals obtained through processes according to variousembodiments in accordance with those described herein may haveadvantageous properties for use as an oxidation catalyst in industrialprocesses. For instance, the NHPI crystals may have particularlydesirable dimensions that make them easier to handle in large volumesand/or at large throughput.

In some embodiments, the NHPI crystals have diameter within the rangefrom 5 μm to 50 μm, preferably within the range from 5 μm to 25 μm, suchas 7 μm to 15 μm, with ranges from any lower limit to any upper limitalso contemplated. The crystals may also or instead have length withinthe range from 100 μm to 600 μm, preferably 150 μm to 600 μm, such as200 μm to 525 μm, with ranges from any lower limit to any upper limitalso contemplated. Preferably, at least 70 wt %, more preferably atleast 80 wt % of the NHPI crystals fall within the foregoing sizedescriptions.

Characterization of the NHPI crystals may be in accordance with anyknown, acceptable method of analysis. However, where differentanalytical methods produce conflicting results, then analytical methodsaccording to the following description shall govern. A Phenom™ G2 pro(available from Phenom-World BV, Eindhoven, The Netherlands) scanningelectron microscope (SEM) with light optical camera and multi-segmentbackscatter detector (BSE), or equivalent equipment, may be used toascertain the measurement. A 100 μm view with a magnification of 530 andfield of view set to 506 μm should be used to measure the dimensions ofthe NHPI crystals. Each view is achieved by using a ½″ slotted head witha carbon adhesive tab. The adhesive tab is pressed into the solidcrystal to obtain a sample for analysis. Compressed air is used todislodge excess material before inserting the slotted head into the SEM,at which time the SEM is zoomed according to the view, magnification,and field of view settings noted above.

Analogous Cyclic Imides

The embodiments described above relating to production of NHPI can alsobe employed using analogous precursors to form other, similar, cyclicimide catalysts with the same active moiety as NHPI. Specifically, it isbelieved that NHPI is a radical mediator capable of assisting in radicalformation during oxidation reaction of various organic species (inparticular, as discussed below, in oxidation of cyclohexylbenzene tocyclohexyl-1-phenyl-1-hydroperoxide). Accordingly, some embodimentsprovide for the formation of a cyclic imide having the following generalformula (I):

wherein X represents an oxygen atom or a hydroxyl group and each of R⁷,R⁸, R⁹, and R¹⁰ is independently selected from: (1) H; (2) C₁ to C₂₀hydrocarbon groups (preferably linear, branched, or cyclic alkyl groups,or aromatic groups); (3) SO₃H; (4) NH₂; (5) OH; (6) a halogen (e.g., F,Cl, Br, I); and (7) NO₂, provided that when any 2 adjacent R-groups areboth C₁ to C₂₀ hydrocarbon groups, such adjacent R groups may be joinedtogether to form cyclic (aliphatic or aromatic) rings. Of course, thecase in which each of R⁷, R⁸, R⁹, and R¹⁰ is H, and X is a hydroxylgroup, corresponds to NHPI. However, other preferred embodiments includeproduction of a compound in which X is OH, and each of R⁷, R⁸, R⁹, andR¹⁰ is independently H or a linear, cyclic, or aromatic alkyl grouphaving 1 to 20, more preferably 1 to 6, carbon atoms. More preferably,each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected from one of: (i) Hand (ii) linear or branched alkyl groups having 1 to 5, more preferably1 to 3, carbon atoms.

Accordingly, instead of phthalic anhydride, analogous carboxylic acidanhydrides corresponding to the above general formula (I) may be reactedwith hydroxylamine in embodiments in accordance with the variousembodiments described herein. That is, embodiments described withreference to “phthalic anhydride” may instead be practiced using,instead of or in addition to the phthalic anhydride, a carboxylic acidanhydride according to the general formula (II):

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is defined as above with referenceto the general formula (I), with the same preferences noted forcarboxylic acid anhydrides of various embodiments.

As will be apparent, the carboxylic acid anhydride of general formula(II) will undergo analogous reaction with hydroxylamine to form anintermediate hydroxamic acid, in a similar manner as seen with phthalicanhydride's reaction with hydroxylamine to form intermediate NHPA, whichis in turn converted to NHPI by heating. The solid intermediatehydroxamic acids of various embodiments are in accordance with thefollowing general formula (III):

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is defined as above with referenceto the general formula (I), with the same preferences noted forhydroxamic acids of various embodiments.

Likewise, the carboxylic acid anhydride of general formula (II) may alsoundergo side reactions to form dicarboxylic acid byproducts havinganalogous structural formula to the byproduct phthalic acid generatedfrom phthalic anhydride, as shown in general formula (IV):

wherein each of R⁷, R⁸, R⁹, and R¹⁰ is defined as above with referenceto the general formula (I), with the same preferences noted fordicarboxylic acid byproducts of various embodiments.Use of the Cyclic Imide as an Oxidation Catalyst

The processes and systems for making cyclic imide catalysts disclosedherein can be used in various oxidation processes. Of particularinterest is the oxidation of cyclohexylbenzene tocyclohexyl-1-phenyl-1-hydroperoxide (also referred to herein ascyclohexylbenzene hydroperoxide). This reaction is of particularinterest when integrated into a process to produce cyclohexanone and/orphenol from benzene via hydroalkylation, as described in, e.g., WIPOPublication Nos. WO 2014/137623 and WO 2016/053583.

Thus, processes of some embodiments may include obtainingcyclohexylbenzene, obtaining a cyclic imide oxidation catalyst (e.g., byany of the methods described herein), and contacting thecyclohexylbenzene and the cyclic imide oxidation catalyst so as toproduce an oxidation effluent comprisingcyclohexylbenzene-hydroperoxide. Such processes may further includecontacting the oxidation effluent with a cleavage catalyst so as toobtain a cleavage effluent comprising phenol and cyclohexanone.

Supply of Cyclohexylbenzene

The cyclohexylbenzene contacted with the cyclic imide oxidation catalystcan be produced and/or recycled as part of an integrated process forproducing phenol and cyclohexanone from benzene. In such an integratedprocess, benzene is initially converted to cyclohexylbenzene by anyconventional technique, including oxidative coupling of benzene to makebiphenyl followed by hydrogenation of the biphenyl. However, inpractice, the cyclohexylbenzene is desirably produced by contactingbenzene with hydrogen under hydroalkylation conditions in the presenceof a hydroalkylation catalyst whereby benzene undergoes the followingReaction (3) to produce cyclohexylbenzene (CHB):

Alternatively, cyclohexylbenzene can be produced by direct alkylation ofbenzene with cyclohexene in the presence of a solid-acid catalyst suchas molecular sieves in the MCM-22 family according to the followingReaction (4):

Side reactions may occur in Reaction (3) or Reaction (4) to produce somepolyalkylated benzenes, such as dicyclohexylbenzenes (DiCHB),tricyclohexylbenzenes (TriCHB), methylcyclopentylbenzene, unreactedbenzene, cyclohexane, bicyclohexane, biphenyl, and other contaminantsThus, typically, after the reaction, the hydroalkylation reactionproduct mixture is separated by distillation to obtain a C₆ fractioncontaining benzene, cyclohexane, a C₁₂ fraction containingcyclohexylbenzene and methylcyclopentylbenzene, and a heavies fractioncontaining, e.g., C₁₈s such as DiCHBs and C₂₄s such as TriCHBs. Theunreacted benzene may be recovered by distillation and recycled to thehydroalkylation or alkylation reactor. The cyclohexane may be sent to adehydrogenation reactor, with or without some of the residual benzene,and with or without co-fed hydrogen, where it is converted to benzeneand hydrogen, which can be recycled to the hydroalkylation/alkylationstep. Depending on the quantity of the heavies fraction, it may bedesirable to either (a) transalkylate the C₁₈s such as DiCHB and C₂₄ssuch as TriCHB with additional benzene or (b) dealkylate the C₁₈s andC₂₄s to maximize the production of the desired monoalkylated species.

Details of feed materials, catalyst used, reaction conditions, andreaction product properties of benzene hydroalkylation, andtransalkylation and dealkylation, can be found in, e.g., Paragraphs[0031], [0032]-[0034], and [0036]-[0048] of WIPO Publication No. WO2016/053583, which description is incorporated by reference herein.

Oxidation of Cyclohexylbenzene

The cyclohexylbenzene (e.g., obtained per the processes described above)is contacted with the cyclic imide oxidation catalyst (e.g., NHPI)obtained from processes consistent with any of those embodimentdescribed herein, whereupon at least a portion of the cyclohexylbenzeneis converted to cyclohexyl-1-phenyl-1-hydroperoxide, the desiredhydroperoxide, according to the following Reaction (5):

The cyclohexylbenzene freshly produced and/or recycled may be purifiedbefore being fed to the oxidation step to remove at least a portion of,among others, methylcyclopentylbenzene, olefins, phenol, acid, and thelike. Such purification may include, e.g., distillation, hydrogenation,caustic wash, and the like.

In exemplary processes, the oxidation may be accomplished by contactingan oxygen-containing gas, such as air and various derivatives of air,with the feed comprising cyclohexylbenzene. For example, a stream ofpure O₂, O₂ diluted by inert gas such as N₂, pure air, or otherO₂-containing mixtures can be pumped through thecyclohexylbenzene-containing feed in an oxidation reactor to effect theoxidation.

Details of the feed material, reaction conditions, reactors used,product mixture composition and treatment, and the like, of theoxidation can be found in, e.g., Paragraphs [0049]-[0071] of WIPOPublication No. WO 2016/053583, which description is incorporated byreference herein.

Cleavage Reaction and Obtaining Phenol and/or Cyclohexanone

At least a portion of the cyclohexyl-1-phenyl-1-hydroperoxide may insome embodiments be subsequently contacted with an acid catalyst so asto decompose at least a portion of thecyclohexyl-1-phenyl-1-hydroperoxide to cyclohexanone and phenolaccording to the following desired Reaction (6):

The cleavage product mixture may comprise the acid catalyst, phenol,cyclohexanone, cyclohexylbenzene, and contaminants.

The acid catalyst preferably is at least partially soluble in thecleavage reaction mixture, is stable at a temperature of at least 185°C., and has a lower volatility (higher normal boiling point) thancyclohexylbenzene.

Feed composition, reaction conditions, catalyst used, product mixturecomposition and treatment thereof, and the like, of this cleavage stepcan be found in, e.g., Paragraphs [0072]-[0084] of WIPO Publication No.WO 2016/053583, which description is incorporated by reference herein.

Further separation and/or processing of the cleavage product mixture,e.g., to obtain phenol and/or cyclohexanone products, may take place asdescribed in Paragraphs [0085]-[00127] of WIPO Publication No. WO2016/053583, which description is incorporated by reference herein.

EXAMPLES Experimental Set-Up

A scaled-down reactor for generating NHPI in a semi-batch process wasset up according to FIG. 3. The equipment 300 included a two-liter glassreactor vessel 320 equipped with a triple propeller 315 on a glassstirring rod 316 coupled to a digital stirring motor 317. One syringepump 321 was used for continuous addition of liquid base solution (NaOHin water or NH₃ in water, as applicable in each experiment describedbelow), and solid doser 305 provided continuous addition of phthalicanhydride crystals into the reactor vessel 320. A heating mantle 325 wasutilized to maintain automated temperature control in the reactor via aheating controller 326 electrically connected to the heating mantle 325and a thermocouple 327 disposed in the reaction medium 330 within thereactor vessel 320. A pH probe 328 was also disposed in the reactionmedium 330 to monitor pH. The bottom of the reaction vessel 320 wasequipped with a two-way valve 340 for slurry drainage through a Buechnerfunnel 350 disposed over a two-liter Erlenmeyer flask 360 maintainedunder vacuum pressure for collection of crude solids.

Analytical Methods

Detailed characterization of the NHPI production samples was performedby high pressure liquid chromatography (HPLC), carbon nuclear magneticresonance spectroscopy (¹³C-NMR), proton nuclear magnetic resonancespectroscopy (¹H-NMR), ion chromatography (IC), inductively coupledplasma elemental analysis (ICP), moisture determination by coulometricKarl Fischer titration (KF), pH tests, temperature measurements, andcrystal dimensions by scanning electron microscopy (SEM).

The HPLC used was an Agilent 1260 in reversed phase; the column was aPhenomenex Kinetex.2.6u Phenyl-Hexyl 100A, 75 mm×2.1 mm, part number00C-4495-AN. Injection volume was 0.3 μL, column temperature was 30° C.,and dual solvents (Solvent A=0.1% Formic Acid, 2.5% MeOH in H₂O; andSolvent B=Methanol) were used with the following Gradient in Table 1:

TABLE 1 HPLC program Solvent A Solvent B Flow rate Time (min) (%) (%)mL/min 0 85 15 0.3 8 85 15 0.3 12 5 95 0.3 17 5 95 0.3 20 85 15 0.3 2585 15 0.3Elution times were as follows: NHPA at 1.1 min, phthalamic acid at 1.3min, phthalic acid at 2.8 min, phenol at 3.2 min, NHPI at 3.6 min,phthalimide at 4.9 min, and phthalic anhydride at 13.1 min. The detectorwas an Ultra-Violet source with diode array detector (DAD) signalscollected at 210, 225 (for quantitative data), and 254 nm. Samples forthe HPLC were prepared in a tarred vial and ethanol was added as adiluent (approx. 2 g of ethanol with 0.002 g of NHPI sample).

Example 1: Hydroxylammonium Salt Reaction with NaOH

Multiple test runs (11) for hydroxylammonium salt reaction with sodiumhydroxide, followed by reaction between hydroxylamine and phthalicanhydride, were carried out according to the following procedures (withtypical observations also reported).

Water (499 g, 21° C.) was added to the reactor vessel 320, followed byaddition of 158 g of hydroxylammonium sulfate ((NH₃OH)₂SO₄) understirring. The liquid reactor content was stirred at 21° C. until thehydroxylammonium sulfate was fully dissolved. Then, over the course of30 minutes, 154 g of a 50 wt % NaOH solution (aqueous) was continuouslyadded to the hydroxylammonium salt solution. Temperature of the reactorcontent was controlled during addition of the NaOH solution such thatmaximum temperature did not exceed 37° C.; stirring speed was set to 300rpm. Stirring continued for 10 minutes after completion of the baseaddition, after which time pH of the reactor content was approximately9.0 and temperature was 35° C.

Solid phthalic anhydride (256 g) was then added to the reactor contentat a rate of 5 g/min under stirring (300 rpm). Temperature rose duringthe addition, and following this addition, heat was applied to thereactor 320 via the external heating mantle 325 such that temperature ofthe reactor content rose to 67° C. at a rate of 1.2° C./min Water wasthen added (575 g, 21° C. water temperature).

By the time reactor content temperature had reached 67° C., formation ofa slurry or butter-like paste was typically observed in the reactorcontent, due to formation and precipitation of solids. The added 575 gwater made the reactor content easier to stir. Upon completion of wateraddition, reactor content temperature was about 45° C.

The reactor content was then heated to 90° C. at 1.2° C./min, andstirred for 15 minutes holding at 90° C. At first, stirring of the 90°C. reactor content was not difficult; however, as NHPI crystals formedduring the heating and stirring (indicated by the transition of thereactor content to a second slurry), stirring became more difficult.After 15 minutes of stirring, the reactor content pH is approximately3.6.

The valve on the bottom of the reactor was then opened, and the 90° C.slurry drained into the settling vessel. The slurry in the settlingvessel was allowed to cool to 21° C. without stirring over the course of20 hours. The slurry was then poured into the Buechner/Erlenmeyer/Vacuumfiltration system to separate the mother liquor from the crude NHPIcrystals. The crude crystals were vacuum filtered for 90 minutes, bywhich time liquid down flow had ceased. The pH of the collected motherliquor was 4.2. The crude crystals were transferred to a vacuum oven(temperature set to 75° C.), and left in the oven for about 6 hours (atwhich time no further weight loss was recorded). Recorded weight ofrecovered NHPI crystals was 215 g.

100 g of the recovered NHPI crystals were removed and further washedwith ice water (4 250 mL washes) to remove any water soluble impurities(e.g., sodium sulfate), followed by another 30 minutes of vacuumfiltration of the crystals. Further heating in the vacuum oven at 75° C.followed for a duration of 20 hours, after which the product wasanalyzed for purity according to the analytical methods notedpreviously.

Example 2: Hydroxylammonium Salt Reaction with NH₃

Two test runs for hydroxylammonium salt reaction with ammonia, followedby reaction between hydroxylamine and phthalic anhydride, were carriedout according to the following procedures (with typical observationsalso reported).

Water (534 g, 21° C.) was added to the reactor, followed by 160 g ofhydroxylammonium sulfate ((NH₃OH)₂SO₄) under stirring. The liquidreactor content was stirred at 21° C. until the hydroxylammonium sulfatewas fully dissolved. Then, over the course of 15 minutes, 127 g of a 29wt % NH₃ solution (aqueous) was added to the hydroxylammonium saltsolution. Temperature of the reactor content was controlled duringaddition of the NH₃ solution such that maximum temperature did notexceed 25° C.; stirring speed was set to 300 rpm. Stirring continued for1 minute after completion of the base addition, after which time pH ofthe reactor content was approximately 9.0 and temperature was 25° C.Times for addition and stirring were substantially lower for NH₃reaction with hydroxylammonium salt as compared to NaOH reaction withhydroxylammonium salt, due to the lower exotherm observed for theNH₃-based reaction; further, it was very easy to maintain thetemperature of the reactor contents at 25° C. instead of 35° C. (as wasthe case with NaOH-based reaction).

Solid phthalic anhydride (259 g) was then added to the reactor contentat a rate of 8 g/min under stirring (300 rpm); again, a lower exothermin the NH₃-based route as compared to NaOH-based route allowed shortertime for this step as compared to the NaOH-based route. Temperature roseduring the addition, and following this addition, heat was applied tothe reactor via the external heating mantle such that temperature of thereactor content rose to 67° C. at a rate of 1.0° C./min. Water was thenadded (542 g, 21° C. water temperature).

By the time reactor content temperature had reached 67° C., formation ofa slurry or butter-like paste was typically observed in the reactorcontent; the 542 g of added water made the reactor content easier tostir. Upon completion of water addition, reactor content temperature wasabout 51° C.

The reactor content was then heated to 90° C. at 1.2° C./min, andstirred for 15 minutes holding at 90° C. At first, stirring of the 90°C. reactor content was not difficult; however, during the course ofstirring, NHPI crystals form, as indicated by the transition of thereactor content to a second slurry forms that makes stirring moredifficult. After 15 minutes of stirring, the reactor content pH wasapproximately 4.3.

The valve on the bottom of the reactor was then opened, and the 90° C.slurry drained into the settling vessel. The slurry in the settlingvessel was allowed to cool to 21° C. without stirring over the course of20 hours. The slurry was then poured into the Buechner/Erlenmeyer/Vacuumfiltration system to separate the mother liquor from the crude NHPIcrystals. The crude crystals were vacuum filtered for 90 minutes, bywhich time liquid down flow had ceased. The pH of the collected motherliquor was 4.6. The crude crystals were transferred to a vacuum oven(temperature set to 75° C.), and left in the oven for about 10 hours (atwhich time no further weight loss was recorded). Recorded weight ofrecovered NHPI crystals was 215 g.

100 g of the recovered NHPI crystals were washed with ice water (4 250mL washes) to remove any water insoluble impurities (e.g., sodiumsulfate), followed by another 30 minutes of vacuum filtration of thecrystals. Further heating in the vacuum oven at 75° C. followed for aduration of 20 hours, after which the product was analyzed for purityaccording to the analytical methods noted previously.

Example 3: Salt-Free Hydroxylamine Solution as Starting Reagent

One test run for salt-free hydroxylamine reaction with phthalicanhydride was carried out according to the following procedures (withtypical observations also reported).

139.4 g of salt-free hydroxylamine aqueous solution (50 wt % in water)were added to the reactor, along with 396 g of water (21° C.) understirring, resulting in a salt-free 13% hydroxylamine aqueous solution.Stirring continued for 10 minutes to ensure proper mixing, after whichtime pH of the reactor content was approximately 8.3 and temperature was21° C.

Solid phthalic anhydride (281 g) was then added to the reactor contentin the reactor at a rate of 9 g/min under stirring (300 rpm).Temperature rose during the addition, and following this addition, heatwas applied to the reactor via the external heating mantle such thattemperature of the reactor content rose to 67° C. at a rate of 1.1°C./min. Water was then added (798 g, 21° C. water temperature).

By the time reactor content temperature had reached 67° C., formation ofa butter-like paste or slurry was typically observed in the reactorcontent; the 798 g of added water made the reactor content easier tostir. Upon completion of water addition, temperature of the reactorcontent was about 45° C.

The reactor content was then heated to 90° C. at 1.2° C./min, andstirred for 15 minutes holding at 90° C. At first, stirring of the 90°C. reactor content was not difficult; however, during the course ofstirring, NHPI crystals formed, as indicated by the transition of thereactor content to a second slurry forms that made stirring moredifficult. After 15 minutes of stirring, the reactor content pH was 3.7.

The valve on the bottom of the reactor was then opened, and the 90° C.slurry drained into the settling vessel. The slurry in the settlingvessel was allowed to cool to 21° C. without stirring over the course of20 hours. The slurry was then poured into the Buechner/Erlenmeyer/Vacuumfiltration system to separate the mother liquor from the crude NHPIcrystals. The crude crystals were vacuum filtered for 90 minutes, bywhich time liquid down flow had ceased. The pH of the collected motherliquor was 3.8. The crude crystals were transferred to a vacuum oven(temperature set to 75° C.), and left in the oven for about 14 hours (atwhich time no further weight loss was recorded). Recorded weight ofrecovered crude NHPI crystals was 222 g. The crystals were then analyzedfor product purity according to the analytical methods noted previously,without water washing.

Analysis and Comparison of Examples 1-3

Table 2 below summarizes the crude product measurements for each Exampleexperiment. Table 3 below summarizes the measurements on recovered solidproduct from Examples 1 and 2 following water wash (again, no water washwas undertaken for Example 3 to demonstrate the relatively high purityobtained without water washing in such processes).

TABLE 2 Crude Solid Analysis Example 1 2 3 Weight of mother liquor (ML)after 1290.2 1271.2 1255.8 Buechner (g) pH of ML 4.2 4.6 3.9 Weight ofsolids after Buechner, 256.5 269.5 258.6 before oven drying (g) Time ofoven drying @ 75° C. 5.9 16.0 14.3 under vacuum (h) Nitrogen flow rateinto oven (SCFH) 0.0 2.0 2.0 Dry product weight (g) 215.3 213.4 221.9Yield (%) on basis of phthalic 72.8 69.6 69.7 anhydride (PAN) reactantYield (%) on basis of HAS precursor 65.3 62.5 n/a to hydroxylaminereactant Yield (%) on basis of hydroxylamine 65.4 62.5 62.6 reactantPhthalic Anhydride conversion to 73.6 70.4 70.1 products + byproductsSulfate content by IC (wppm) 19006 27921 34 Chloride by IC (wppm) 1449893 965 Na⁺ or NH₄ ⁺ calculated 10096 10940 504 or by ICP (ppm) Watercontent by KF (wt %) 0.53 1.67 1.88 Organic impurities by NMR (%) 1.301.50 1.00 pH of 1000 ppm dry product in 4.33 4.5 4.4 DI water ML (g) -max (calculated) 1437 1424 1400 ML N content (ppm) - max 6501 28484 7907(calculated) ML Na content - max (calculated) 30732 0 0 ML SO₄ content -max (calculated) 64275 65690 0 ML C content - max (calculated) 3165236164 39816 Purity of crude crystals (NHPI, wt %) 95.1 93.0 97.0

TABLE 3 Solid Analysis After Water Wash of 100 g of Crystals Example 1 2water per wash (g) 250.0 250.0 # washing steps 4.0 4.0 Temp of water (°C.) 1.5 5.2 Time of last Buechner filtration under vacuum (min) 30.015.0 NHPI before wash (g) 100.1 150.1 Time of product drying @ 75° C.under vacuum (h) 21.0 24.8 Final dry product wt (g) 93.6 142.2 Yield (%)on basis of PAN reactant 69.8 69.1 Yield (%) on basis of HAS precursorto HA reactant 62.6 62.0 Sulfate content by IC (wppm) 19 159.0 Chloridecontent by IC (wppm) 1606.1 810.0 Sodium content by ICP (ppm) 373.5471.8 Water content by KF (wt %) 0.28 1.7 Organic impurities by NMR (wt%) 0.0 0.0 pH of 1000 ppm dry NHPI in DI water 4.27 4.7 Purity (NHPI, wt%) 99.5 98.1

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present invention. The contents of all referencescited herein are incorporated by reference in their entirety.

The invention claimed is:
 1. A process comprising: (a) contacting a hydroxylamine solution with a cyclic carboxylic acid anhydride so as to form a reaction medium having initial temperature T_(i) of less than 65° C.; (b) raising the reaction medium temperature to a transition temperature T_(t) within the range from 65° C. to less than 75° C., thereby forming a first slurry comprising solid intermediate hydroxamic acid within the reaction medium; (c) further heating the reaction medium to a final temperature T_(f) within the range from 75° C. to 200° C., thereby converting at least a portion of the solid intermediate hydroxamic acid to solid cyclic imide, such that the reaction medium comprises a second slurry comprising the solid cyclic imide; wherein the cyclic carboxylic acid anhydride has the general formula (II)

and further wherein the cyclic imide has the general formula (I)

where, in each formula (I) and (II), X is an oxygen atom or a hydroxyl group, and further wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected from: (1) H; (2) C₁ to C₂₀ linear, cyclic, or aromatic hydrocarbon groups; (3) SO₃H; (4) NH₂; (5) OH; (6) a halogen; and (7) NO₂; wherein the process comprises continuously feeding the hydroxylamine solution and carboxylic acid anhydride to a continuous flow reactor via one or more feed inlets, so as to establish the reaction medium flowing continuously in a downstream direction within the continuous flow reactor; at a second location along the continuous flow reactor that is downstream of the one or more feed inlets, feeding steam or water into the reaction medium; at a third location along the continuous flow reactor that is downstream of the second location, feeding additional steam or additional water into the reaction medium; agitating the reaction medium within the continuous flow reactor between the second and third locations; and recovering a reaction product comprising solid cyclic imide from the reaction medium; and wherein, the continuous flow reactor is in fluid communication with (i) a first steam conduit and (ii) a second steam conduit downstream of the first steam conduit, wherein (b) raising the reaction medium temperature to the transition temperature T_(t) comprises adding steam to the reaction medium through the first steam conduit, and wherein (c) further heating the reaction medium to the final temperature T_(f) comprises adding additional steam to the reaction medium through the second steam conduit.
 2. The process of claim 1, wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected from one of: (i) H and (ii) linear or branched alkyl groups having 1 to 5 carbon atoms.
 3. The process of claim 2, wherein the carboxylic acid anhydride is phthalic anhydride, the intermediate hydroxamic acid is N-hydroxyphthalamic acid (NHPA), and the cyclic imide is N-hydroxyphthalimide (NHPI).
 4. The process of claim 1, wherein the temperature of the reaction medium is raised from the initial temperature T_(i) to the transition temperature T_(t) at a rate within the range from 0.01 to 500° C./min.
 5. The process of claim 1, further comprising monitoring the temperature of the reaction medium at a first location and, based at least in part upon the temperature at the first location, controlling one or both of (i) reaction medium flow rate in the continuous flow reactor and (ii) flow rate of the steam through the first conduit in order to raise the reaction medium temperature to the transition temperature T_(t).
 6. The process of claim 5, wherein the controlling results in raising the reaction medium temperature from the initial temperature T_(i) to the transition temperature T_(t) at a rate within the range from 0.01 to 500° C./min.
 7. The process of claim 1, further comprising monitoring the temperature of the reaction medium at a second location and, based at least in part upon the temperature at the second location, controlling one or both of (i) reaction medium flow rate in the continuous flow reactor and (ii) flow rate of the additional steam through the second steam conduit in order to raise the reaction medium temperature to the final temperature T_(f).
 8. The process of claim 1, wherein the hydroxylamine solution comprises (a) 30-70 wt % hydroxylamine, (b) water, and (c) less than 1 wt % of compounds other than hydroxylamine and water.
 9. The process of claim 1, wherein the hydroxylamine solution is formed by a process comprising: (a-1) contacting a hydroxylammonium salt with an aqueous base to form at least a portion of said hydroxylamine solution.
 10. The process of claim 9, wherein the hydroxylammonium salt is hydroxylammonium sulfate.
 11. The process of claim 9, wherein the aqueous base is selected from the group consisting of sodium hydroxide and ammonia.
 12. The process of claim 1, wherein the solid cyclic imide comprises NHPI crystals having diameter within the range from 5 μm to 50 μm, and length within the range from 200 μm to 525 μm.
 13. The process of claim 1, further comprising providing at least a portion of the solid cyclic imide to an oxidation reaction.
 14. The process of claim 1, further comprising contacting at least a portion of the solid cyclic imide with cyclohexylbenzene and an oxygen-containing gas so as to obtain cyclohexyl-1-phenyl-1-hydroperoxide.
 15. A process comprising: (a) contacting a hydroxylamine solution with a cyclic carboxylic acid anhydride so as to form a reaction medium having initial temperature T_(i) of less than 65° C.; (b) raising the reaction medium temperature to a transition temperature T_(t) within the range from 65° C. to less than 75° C., thereby forming a first slurry comprising solid intermediate hydroxamic acid within the reaction medium; (c) further heating the reaction medium to a final temperature T_(f) within the range from 75° C. to 200° C., thereby converting at least a portion of the solid intermediate hydroxamic acid to solid cyclic imide, such that the reaction medium comprises a second slurry comprising the solid cyclic imide; wherein the cyclic carboxylic acid anhydride has the general formula (II)

and further wherein the cyclic imide has the general formula (I)

where, in each formula (I) and (II), X is an oxygen atom or a hydroxyl group, and further wherein each of R⁷, R⁸, R⁹, and R¹⁰ is independently selected from: (1) H; (2) C₁ to C₂₀ linear, cyclic, or aromatic hydrocarbon groups; (3) SO₃H; (4) NH₂; (5) OH; (6) a halogen; and (7) NO₂; wherein the process comprises continuously feeding the hydroxylamine solution and carboxylic acid anhydride to a continuous flow reactor via one or more feed inlets, so as to establish the reaction medium flowing continuously in a downstream direction within the continuous flow reactor; at a second location along the continuous flow reactor that is downstream of the one or more feed inlets, feeding steam or water into the reaction medium; at a third location along the continuous flow reactor that is downstream of the second location, feeding additional steam or additional water into the reaction medium; agitating the reaction medium within the continuous flow reactor between the second and third locations; and recovering a reaction product comprising solid cyclic imide from the reaction medium; (d) obtaining from the second slurry (i) a plurality of solid cyclic imide crystals and (ii) a wastewater effluent comprising a dicarboxylic acid byproduct having the general formula (III):

wherein obtaining the plurality of solid cyclic imide crystals and the wastewater effluent comprises: (d-1) collecting at least a portion of the second slurry comprising solid cyclic imide crystals and mother liquor on a filtration belt; (d-2) passing the filtration belt having solid cyclic imide crystals disposed thereon over one or more vacuum devices; (d-3) contacting the solid cyclic imide crystals disposed on the filter belt with wash water having temperature within the range from 0° C. to 30° C.; (d-4) contacting the solid cyclic imide crystals disposed on the filter belt with drying steam and then with an inert gas, such that at least a portion of the drying steam condenses on the solid cyclic imide crystals; (d-5) after carrying out (d-1) through (d-4), collecting the solid cyclic imide crystals in a solid conveyor; (d-6) collecting at least a portion of the mother liquor; (d-7) collecting at least a portion of each of the wash water, condensed drying steam, and inert gas after each contacts the solid cyclic imide crystals; and (d-8) combining said portions of each of the mother liquor, wash water, condensed drying steam, and inert gas to form the wastewater effluent.
 16. The process of claim 15, further comprising: (e) contacting the wastewater effluent with a strong acid, thereby precipitating solid dicarboxylic acid byproduct from the wastewater effluent; recovering the precipitated dicarboxylic acid byproduct from the wastewater effluent by solid/liquid separation; and (g) dehydrating at least a portion of the recovered dicarboxylic acid byproduct so as to form additional cyclic carboxylic acid anhydride.
 17. The process of claim 16, wherein the additional cyclic carboxylic acid anhydride constitutes at least part of the cyclic carboxylic acid anhydride contacted with the hydroxylamine solution in (a).
 18. The process of claim 15, wherein the dicarboxylic acid byproduct comprises phthalic acid. 